Those seizures are then cited by federal prosecutors when they ask judges to lengthen prison sentences for the lookouts.

Because scouts are accused of conspiring to smuggle large amounts of marijuana they don't possess when arrested, prosecutors often allow suspected scouts to plead guilty to conspiring to smuggle one backpack-load of marijuana, or about 40 pounds (18 kilograms).

But when agents report large seizures, the plea offer is upped to two backpack-loads or more, prosecutors wrote in sentencing memorandums.

The Star searched online court records since the start of 2015 and found nine scout prosecutions in the last year, including six since October, where prosecutors cited large marijuana seizures by Border Patrol agents and used those seizures to request longer sentences.

The strategy has increased a typical plea offer for a scout with no criminal history from six months to 13 months.

The U.S. Attorney's Office has wrestled for at least four years with how to prosecute drug scouts.

"The reason pleas are climbing is we're realizing and being able to prove how important these people are," federal prosecutor Adam Rossi told Judge James A. Soto at a Feb. 7 sentencing hearing in U.S. District Court in Tucson. "We have a better understanding and actual marijuana to show how important scouts are to these organizations. Without them, the billions of dollars that are made by the cartels would not be possible."

The role of a scout is to act as an "air traffic controller" for groups of marijuana backpackers in the desert west of Tucson, Border Patrol Agent Carlos Rochin testified at a February 2016 hearing in federal court in Tucson.

As backpacker groups make their way across the valley below, the scouts watch for law enforcement officers and makes sure the groups are staggered enough to not draw attention, according to a 32-page transcript of Rochin's testimony.

Scouts "hold the groups until a couple of them have gone through and then keep the flow regulated," Rochin said.

Some backpackers are professional smugglers, while a "good portion" are migrants who cannot afford to pay the smuggler's fee to cross the border and agree to haul marijuana instead, Rochin said.